1. Field of the Invention
The present invention relates to a stack type surface acoustic wave package, and a method for manufacturing the same. More particularly, the present invention relates to a stack type surface acoustic wave package, which is formed by packaging two piezoelectric single crystal bare chips formed of the same material to face each other through a chip-scale packaging process and a wafer level packaging process, thereby allowing integration of two filters having different frequency bands and high resistance to thermal impact into a single component while reducing a product size, and a method for manufacturing the same.
2. Description of the Related Art
As communication technology has advanced remarkably in recent years, miniaturization, high performance, and multifunctionality are required for mobile communication products. In order to achieve theses requirements, various components, for example, a filter, a duplexer, and the like, used for the mobile communication products are also required to be miniaturized and multi-functionalized.
As for one example of these components, a surface acoustic wave device comprises a piezoelectric board 1 which is a piezoelectric single crystal bare chip, a pair of Inter-Digital Transducer (IDT) electrodes 2 facing each other in an interdigitated pattern on the piezoelectric board 1, and input and output electrodes 3 and 4 connected to the IDT electrodes 2, respectively.
When an electric signal is applied through the input electrode 3, the piezoelectric effect causes piezoelectric distortion to occur corresponding to an overlap length between the IDT electrodes 2, and the piezoelectric distortion generates surface acoustic waves, which are transmitted to the piezoelectric board 1. Then, the surface acoustic waves are converted into an electric signal, and output through the output electrode 4. At this time, only the electric signal having a predetermined frequency band determined by various factors, such as distance between the IDT electrodes 2, width or length of the IDT electrodes 2, is filtered out.
As such, the surface acoustic wave device has characteristics determined by the distance between the IDT electrodes 2, the width or length of the IDT electrodes 2 formed on the piezoelectric board 1 of the surface acoustic wave device. If the IDT electrodes 2 are damaged or have minute foreign substances such as dust attached thereto, the characteristics of the device will be changed. Thus, various package structures are required to protect the electrodes of the surface acoustic wave device from the external environment.
A fundamental structure of a conventional surface acoustic wave package comprises a ceramic wiring board, devices mounted on the board, and a sealing member packaging the devices and the board, as shown in FIGS. 2a, 2b and 2c. 
In FIG. 2a, a surface-mount type surface acoustic wave package 10 comprises a wiring board 11 formed of a plurality of staked ceramic layers, a device 15 having input, output and IDT electrodes 15a, 15b and 15c formed thereon, and a lid 19 mounted on the wiring board 11 to seal the device 15 in a cavity formed when the plurality of ceramic layers are stacked to form the wiring board 11, in which the device 15 is connected in a wire-bonding manner to via-holes 12 passing through the wiring board 11 via a plurality of metal wires 13 such that the electrodes 15a, 15b and 15c face the lid 19 in the cavity.
In FIG. 2b, a flip-chip bonding type surface acoustic wave package 20 comprises a wiring board 21, a device 25, and a lid 29, in which the device 25 is connected in a flip chip-bonding manner to via-holes 22 passing through the wiring board 21 via a plurality of bump balls 23 such that electrodes 25a, 25b and 25c face the board 21 in a cavity, and in which the device 25 is sealed in the cavity on the wring board 21 by the lid 29.
In FIG. 2c, a chip-scale packaging type surface acoustic wave package 30 comprises a wiring board 31, a device 35, and a metal layer 39, in which the device 35 is connected in a flip chip-bonding manner to via-holes 32 passing through the wiring board 31 via a plurality of bump balls 33 such that electrodes 35a, 35b and 35c face the wiring board 31, and in which the device 35 mounted above the wiring board 31 is sealed by a laminated film 38 and the metal layer 39 applied to an upper surface of the film 38.
The conventional packages 10 and 20 are formed by mounting the devices 15 and 25 on the wiring boards 11 and 21, each of which has the cavity formed by stacking two or more ceramic layers, and then sealing the cavity using the metal lids 19 and 29 welded to the boards 11 and 21. As a result, the conventional packages 10 and 20 are expensive due to material costs, have lots of components and limit reduction in product size, failing to achieve product miniaturization.
Meanwhile, in FIG. 7, a surface acoustic wave package 40 can filter out different frequency bands. The surface acoustic wave package 40 is formed by mounting two devices 45 and 46 on a wiring board 51 having via-holes 42 passing therethrough via bump balls 43 in which IDT electrodes of the devices 45 and 46 are different in width, length and distance therebetween, and then sealing the devices using a laminated film 48 and a metal layer 49.
However, since the conventional surface acoustic wave package 40 has the two devices 45 and 46 having different thicknesses, and the two devices 45 and 46 are horizontally disposed on the single wiring board 41, there is a problem in that the overall size of the product is remarkably increased.
Additionally, since the thermal expansion coefficient of the ceramic wiring board is about 7 mm/m2K, and the thermal expansion coefficient of the piezoelectric single crystal bare chip is about 15 mm/m2K, there is a difference in thermal expansion coefficient between the materials. Thus, when welding the metallic lid or when wire-bonding or flip-chip bonding the input and output electrodes of the device to the via-holes of the wiring board, thermal impact applied from the outside frequently causes damage, such as separation of the bump ball or a bonding surface between the device and the board.